Sensor arrangement

ABSTRACT

Disclosed is a sensor arrangement which is especially suitable for detecting if the windscreen of a motor vehicle is steamed up. The sensor arrangement comprises a heat conducting layer disposed on a supporting surface. Said layer exhibits good heat conducting properties. A support plate is arranged on top of the heat conducting layer, comprising a recess and several electrical conductor tracks. A moisture-sensitive sensor element is arranged in the region of the recess of the support plate. Said sensor element is electroconductively connected to the conductor tracks on the support plate. The inventive arrangement ensures that the temperature difference between the sensor element and the supporting surface does not go beyond a given limit when measurement occurs.

[0001] The present invention is directed to a sensor system which is suited, in particular, for detecting the fogging of the inside of a motor-vehicle windshield.

[0002] Numerous approaches are known for avoiding the fogging of windshields in automobiles. U.S. Pat. No. 4,408,660, for instance, proposes regulating the motor-vehicle air-conditioning system on the basis of output signals from many different types of sensors, in order to prevent fogging. Among the sensors used or required is a humidity sensor, which measures the relative humidity or the dew point on the particular motor-vehicle windshield. However, this publication does not include any further references to the specific embodiment of the humidity sensor. Moreover, the proposed control concept requires at least one further sensor for measuring the temperature, so that considerable outlay is entailed for sensor technology.

[0003] Another approach for dealing with the above problem provides for using an infrared sensor to determine the surface temperature of one region of the automobile windshield. With the aid of this sensor and other humidity sensors in the passenger compartment, the humidity and/or the temperature of the passenger compartment can be regulated via the motor-vehicle air-conditioning system, to reliably prevent the windshields from fogging up. The drawback of this variant is likewise the substantial outlay for sensor technology.

[0004] In summary, therefore, existing approaches typically require a multiplicity of sensors to reliably sense the fogging of the motor-vehicle windshield.

[0005] The object of the present invention is, therefore, to provide a sensor system that is simple to construct and is suited for reliably sensing the fogging of a supporting surface, in particular of a motor-vehicle windshield.

[0006] This objective is achieved by a sensor system having the features set forth in claim 1.

[0007] Advantageous further refinements of the sensor system according to the present invention are derived from the measures delineated in the dependent claims.

[0008] The proposed measures ensure that, with the aid of a single sensor system according to the present invention, it is possible to reliably sense and, therefore, prevent the fogging of a supporting surface, for example the inside of a motor-vehicle windshield. For this purpose, the output signals from the sensor system according to the present invention are fed to a corresponding climate control, i.e., to a controlled air-conditioning system. The sensor system according to the present invention merely detects the relative humidity on the supporting surface. It is ensured, in this connection, that the sensor element used precisely detects the actual relative humidity on the supporting surface, since, in the measuring operation, the sensor element has virtually the same temperature as the supporting surface. Various measures are applied to make certain that there is merely a slight temperature differential between the supporting surface and the sensor element.

[0009] Thus, the sensor system according to the present invention provides a reliable way to overcome the fogging problem discussed above, while entailing minimal outlay for sensory technology.

[0010] Moreover, by eliminating additional sensor elements, there are altogether fewer system errors. This is because, ultimately, each individual sensor element contributes to the overall error in the context of detecting fogging. The result is greater system accuracy and reliability.

[0011] Further advantages of the sensor system according to the present invention and details pertaining thereto are derived from the following description of exemplary embodiments, on the basis of the figures.

[0012] The Figures show:

[0013]FIG. 1 a perspective view of a motor-vehicle windshield, including a first specific embodiment of the sensor system according to the present invention;

[0014]FIGS. 2a and 2 b, each, a part-sectional view of the sensor system of FIG. 1;

[0015]FIG. 3 a part-sectional view of a second specific embodiment of the sensor system according to the present invention.

[0016]FIG. 1 shows a part of the inside of a motor vehicle windshield 1, which, in this exemplary embodiment, is used as a supporting surface and whose fogging is to be prevented. Sensor system 10 is mounted on the side of motor-vehicle windshield 1 facing the passenger compartment; in this context, FIG. 1 shows a first specific embodiment of such a sensor system. The output signals from sensor system 10 are fed via a connecting cable 20 to a controlled motor-vehicle air-conditioning system (not shown). On the basis of the delivered humidity-dependent sensor signals, the air-conditioning system prevents the inside of motor-vehicle windshield 1 from fogging and, thus, a potential sight obscuration. For this reason, it is possible to vary the heating temperature and/or the ventilation flow rate in a generally known, defined way, via the motor-vehicle air-conditioning system.

[0017] Using sensor system 10 according to the present invention, at this point, it is merely the relative air humidity that is determined on that side of motor-vehicle windshield 1 on which sensor system 10 is mounted. As soon as a predefined limiting value for the relative air humidity RH, e.g., RH=95%, is exceeded, as previously indicated, appropriate counter-measures are taken in terms of control engineering, via the motor-vehicle air-conditioning system. In comparison to previous fog-prevention approaches which always focused on determining the dew point on the motor-vehicle windshield, sensor system 10 according to the present invention offers a comprehensive approach based on simple sensory technology. In particular, the approach according to the present invention manages without additional sensors, such as temperature sensors, etc.

[0018] In FIG. 1, of sensor system 10 according to the present invention, one can discern a support plate 11, on which is mounted a humidity-sensitive sensor element 12 over a recess 15, as well as further electronic components 13 a-13 e. Support plate 11 is designed as a conventional circuit plate of FR4 material and does not contain any electrical conductor tracks for contacting the components mounted thereon. The thickness of support plate 11 that is used is preferably within the range of 1-2 mm. Via connecting cable 20, sensor system 10 is connected to the downstream signal-processing unit, for example to a corresponding climate control of the motor-vehicle air-conditioning system. In this context, connecting cable 20 may be detachably connected to support plate 11, for example using an appropriate connector.

[0019] In the present example, sensor element 12 is designed as a known capacitive thin-film humidity sensor, which has a dielectric, e.g., a suitable polymer material, between two electrodes, which changes its capacitance as a function of humidity. The electrodes and dielectric are usually placed on a suitable carrier substrate, such as glass. Accordingly, on the output side, sensor element 12 supplies electric signals in a generally known manner. They are a measure of the relative humidity in the particular ambient environment.

[0020] As is discernible in FIG. 1, sensor element 12 is positioned in the vicinity of a rectangular recess 15 of support plate 11. Via recess 15 in support plate 11, a certain air circulation is ensured in the area of the sensor. The longitudinal axis of rectangular recess 15 is aligned perpendicularly to the longitudinal axis of sensor element 12. In this specific embodiment of the present invention, sensor element 12 is positioned on that side of support plate 11 which is oriented so as to face away from windshield 1. For that reason, sensor element 12, as well as the other components 13 a-13 e on support plate 11, are designed as SMD components. Thus, on that side in the area of bearing surface on support plate 11, sensor element 12 has electrically conductive contacts, which face support plate 11. In this manner, a simple, efficient fabrication of sensor system 10 is ensured, in particular, since support plate 11 is then able to be populated in automated fashion.

[0021] Likewise discernible in FIG. 1 is that sensor element 12 has a rectangular form and, at least in one dimension, is greater in length than recess 15, so that sensor element 12 rests in two contact areas on support plate 11.

[0022] The additionally provided components 13 a-13 e on support plate 11 are used for processing the output signals from sensor element 12. A further signal processing of this kind may be implemented, for instance, in the form of a signal amplification; in addition, the conversion into a simply transmittable and further processable signal may be provided; further components may be used for protecting sensor system 10 from electrical overvoltages and disturbing electromagnetic influences, etc. The various electronic components 13 a-13 e are provided on support plate 11 with a protective coating, which protects them from mechanical influences, as well as from humidity and pollution, etc. A protective lacquer manufactured by the firm Grace, marketed under the type designation Eccocoat, is suited for this purpose.

[0023] To further clarify the first exemplary embodiment of the sensor system according to the present invention, reference is made to FIGS. 2a and 2 b, which each show a part-sectional view of sensor system 10 of FIG. 1 in the vicinity of recess 15 of support plate 11. Shown here, in turn, is motor-vehicle windshield 1 having sensor system 10 positioned thereon.

[0024] As is apparent in FIG. 2a, support plate 11 is secured in this specific embodiment via a thermally conductive layer 14 to motor-vehicle windshield 1, i.e., to the supporting surface. In the illustrated exemplary embodiment, thermally conductive layer 14 has various functions. Of primary significance here is, preferably, the best possible thermal conduction of this layer 14; furthermore, in this variant, thermally conductive layer 14 also acts as a fastening means for support plate 11 mounted thereon and for sensor element 12.

[0025] In one advantageous specific embodiment, the thermally conductive layer or adhesive layer is formed as a doubly-sided cementing adhesive film, as is available from the firm 3M under the type designations 9882, 9885 or 9890. An important consideration in selecting a suitable adhesive layer in this context is that it preferably have the most efficient possible thermal conduction properties. The customary thickness of the adhesive layer varies, depending on the type used, for instance between 0.05 mm and 0.25 mm.

[0026] Positioned above recess 15 is humidity-sensitive sensor element 12. No further details pertaining thereto are discernible in this illustration. Suitable sensor elements 12 are marketed by the Applicant under the type designations HC102 or HC103. In FIG. 2a, on the bottom side of sensor element 12, reference numerals 12 a, 12 b schematically denote the electrically conductive contacts, which are used to make electrical contact with and connect to the conductor tracks in support plate 11. Contacts 12 a, 12 b are situated in sensor element 12 in the contact area, where it rests on support plate 11 outside of recess 15.

[0027] Sensor element 12,used, which in this exemplary embodiment is designed as an SMD component, has a humidity-sensitive surface, which, in the same way as contacts 12 a, 12 b, is oriented toward support plate 11. Accordingly, in this specific embodiment of a humidity-sensitive sensor element 12, contacts 12 a, 12 b are positioned on the same side.

[0028] Likewise discernible in FIG. 2a in support plate 11 are vertical bores 16 a, 16 b which are placed so as to be directly adjacent to recess 15. Via these bores 16 a, 16 b, an efficient thermal conduction is ensured between the supporting surface, i.e., windshield 1 and sensor element 12. In the plan view of a subsection of the sensor system in FIG. 2b, it is discernable that, in this exemplary embodiment, a multiplicity of such bores 16 a-16 h are positioned adjacently to recess 15.

[0029] The diameters of bores 16 a-16 h are preferably selected to be identical to the diameters of the vias or bores otherwise provided on support plate 11, i.e., diameters between 0.3 mm and 0.8 mm are selected. Also preferable—as discernible in FIG. 2b—is a plurality of separate bores 16 a-16 h having smaller diameters, instead of fewer bores having larger diameters in support plate 11.

[0030] In addition, in this exemplary embodiment, the various bores 16 a-16 h have a coating having preferably good heat conduction properties, for example a copper coating, in the bore region, to ensure an excellent thermal conduction between supporting surface 1 and sensor element 12 via bores 16 a-16 h. The thermally conductive coating in the bore region is preferably formed to be as thick as possible, for instance thicker than 30 μm. An additional tinning of a copper coating of this kind further improves the thermally conductive properties.

[0031] Finally, it proves to be advantageous with respect to thermal conduction when such thermally conductive coatings of bores 16 a, 16 b are thermally conductively interconnected on that side of support plate 11, which is oriented in the direction of sensor element 12. For this, a corresponding coating 17 of support plate 17 in a surface area around sensor element 12 and its terminal contacts 12 a, 12 b may be provided, as is perceivable in FIG. 2b. In this manner, a thermally conductive connection is established between the various bores 16 a-16 h.

[0032] Bores 16 a-16 h in support plate 11, as well as the use of thermally conductive layer 14 having excellent heat-conduction properties, ensure in this exemplary embodiment that sensor element 12 and supporting surface 1, i.e., the inside of the windshield in measuring operation, have a substantially identical temperature. In addition, in this exemplary embodiment of the sensor system according to the present invention, the design of sensor element 12 as an SMD component also contributes to the efficient thermal coupling, since this ensures an intimate thermal contact to the layers placed before sensor element 12.

[0033] It is, therefore, important for sensor system 10 according to the present invention to have a best possible thermal contact between the side of windshield 1 on which fogging is to be prevented, and sensor element 12. It must be provided at the least, however, that a specific—preferably as low as possible—temperature difference between supporting surface 1 and sensor element 12 not be exceeded during measuring operation. In the present example, a maximum temperature difference of about 0.5° C. results between the side of windshield 1 facing sensor element 12, and sensor element 12. Such a temperature gradient is still considered as not being critical to the measurement.

[0034] A further measure for optimizing the heat-conduction properties in this area of sensor system 10, in addition to the measures discussed above in connection with the borehole coating, would be, for instance, providing an additional, efficiently thermally conductive surface coating on that side of. support plate facing thermally conductive layer 14, and at least in the bore region.

[0035] A second specific embodiment of the sensor system according to the present invention is elucidated in the following on the basis of FIG. 3, which, in turn, shows a part-sectional view of the sensor system.

[0036] Mounted, in turn, on the inside of motor-vehicle windshield 100, i.e., on the corresponding supporting surface whose fogging is to be prevented, is sensor system 110 according to the present invention. As in the first exemplary embodiment, this includes a thermally conductive layer 114, formed as an adhesive layer, and, placed over it, a support plate 111 having a recess 115. Humidity-sensitive sensor element 112 is placed on thermally conductive layer 114 in the vicinity of recess 115. Also schematically indicated in FIG. 3 is an electronic component 113 a, which is used for further signal processing and is mounted on that side of support plate 111 which is oriented so as to face away from the motor vehicle windshield 100.

[0037] With respect to suitable materials for the adhesive layer and for the support plate, reference is made at this point merely to the preceding example.

[0038] As a variation of the preceding example, sensor element 112 is positioned or placed in sensor system 110 according to the present invention. Thus, sensor element 112 in the area of recess 115 is directly positioned on thermally conductive layer 114 formed as an adhesive layer, the humidity-sensitive surface of sensor element 112 being oriented so as to face away from the motor-vehicle windshield. An SMD thin-layer humidity sensor is directly positioned, for example, on a doubly-sided cementing adhesive film, the humidity-sensitive surface of sensor element 112 being oriented toward support plate 111.

[0039] Sensor element 112 is electrically contacted from that side of sensor element 112 which is oriented so as to face away from motor-vehicle windshield or supporting surface 100. To this end, contacts 112 a, 112 b, via which the connection to the electrical conductor tracks in support plate 111 is made, are positioned on this side of sensor element 112. Accordingly, in this specific embodiment of sensor system 110 according to the present invention, the same humidity-sensitive SMD sensor element may be used as in the preceding example; merely the orientation of the humidity-sensitive surface or of contacts 112 a, 112 b is now selected to face away from the windshield.

[0040] Alternatively to the illustrated variant, it is also fundamentally possible to use bonding wires for electrical contacting, via which the contacts of the sensor element are electrically connected to the conductor tracks in the support plate.

[0041] What is advantageous about the variant of the sensor system according to the present invention illustrated in FIG. 3 is that sensor element 112 is now placed even closer to that side of motor-vehicle windshield or supporting surface 100 where a potential fogging is to be detected. It is thus ensured to an even greater degree that a smallest possible temperature difference results between sensor element 112 and supporting surface 100, i.e., that they exhibit nearly the same temperature as they do during measuring operation.

[0042] In a further specific embodiment (not shown) of the present invention, it may finally be provided to replace the thermally conductive layers formed as an adhesive layer, of the two first explained variants, with a layer which merely has excellent thermal conductivity, but which is designed to be non-adhesive. Suited for this are, for example, ceramic-filled polymer films distributed under the designation Keratherm by the firm Kerafol, Keramische Folien GmbH. In such a case, appropriate mechanical fasteners must be used to secure the sensor system to the windshield or the supporting surface. For this, it may be provided, for example, to use the base of a rearview mirror as a fastening means; alternatively, a gap at the top windshield edge between the vehicle cover and the windshield may be used as a mechanical fastening means, etc.

[0043] The present invention is, therefore, not limited to the described embodiments; rather, within the scope of the considerations according to the present invention, there are a number of other variants of embodiments. 

1. A sensor system for mounting on a supporting surface, comprised of: a thermally conductive layer (14) having good thermal conductivity which may be positioned on the supporting surface (1), a support plate (11) on the thermally conductive layer (14), the support plate (11) including at least one recess (15) as well as a plurality of electrical conductor tracks, a humidity-sensitive sensor element (12) which is positioned in the vicinity of the recess (15) of the support plate (11) and which is electroconductively connected to the conductor tracks on the support plate (11), wherein the sensor element (12) is positioned on that side of the support plate (11), above the recess, which is provided for being oriented averted from the supporting surface (1) and the support plate (11) has one or more bores (16 a-h) adjacent to the recess (15), the bores (16 a-h) being furnished with a thermally conductive layer, so that it is ensured that between the sensor element (12) and the supporting surface (1) a predefined temperature difference is not exceeded in the measuring operation, and fastening means for fastening the support plate (11) and the sensor element (12) on the supporting surface (1) are present.
 2. The sensor system as recited in claim 1, wherein the inside of a motor-vehicle pane facing the passenger compartment acts as a supporting surface (1).
 3. The sensor system as recited in claim 1, wherein further components (13 a, . . . 13 e) for processing output signals from the sensor element (12) are mounted on the support plate (11).
 4. The sensor system as recited in claim 3, wherein the components (13 a, . . . 13 e) are provided with a protective coating.
 5. The sensor system as recited in claim 1, wherein the support plate (11) has a detachable connection to a connecting cable (20).
 6. The sensor system as recited in claim 1, wherein the support plate (11) is made of FR4 material.
 7. The sensor system as recited in claim 1, wherein the thermally conductive layer (14) is formed as a doubly-sided cementing adhesive film, which is simultaneously used as a fastening means.
 8. The sensor system as recited in claim 1, wherein the sensor element (12) is designed as a capacitive thin-film humidity sensor, which has a humidity-sensitive dielectric placed between a plurality of electrodes, and has a humidity-sensitive surface which is oriented toward the support plate (11).
 9. The sensor system as recited in claim 1, wherein it is ensured by the set-up and formation of the various elements of the sensor system (10) that a temperature difference of 0.5° C. between the sensor element (12) and the supporting surface (1) is not exceeded during measuring operation.
 10. The sensor system as recited in claim 1, wherein the sensor element (12) is designed as an SMD component and, on that side facing the support plate (11), has electrically conductive contacts (12 a, 12 b) for connecting to the conductor tracks of the support plate (11).
 11. The sensor system as recited in claim 10, wherein the sensor element (12), at least in one dimension, is designed to be greater in length than the recess (15), and the electrically conductive contacts (12 a, 12 b) are situated in the contact areas outside of the recess (15).
 12. The sensor system as recited in claim 1, wherein the thermally conductive coating is made of copper.
 13. The sensor system as recited in claim 1, wherein the coating (17) is also placed in a specific surface area on at least one side of the support plate (11), and a thermally conductive connection is established between the various bores (16 a-16 h).
 14. The sensor system as recited in claim 1, wherein the fastening means are designed as mechanical fastening means. 